Journal articles on the topic 'Jones Corner fault zone'
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1
Aksoy, R., and A. Demiröz. "The Konya earthquakes of 10–11 September 2009 and soil conditions in Konya, Central Anatolia, Turkey." Natural Hazards and Earth System Sciences 12, no. 2 (February 10, 2012): 295–303. http://dx.doi.org/10.5194/nhess-12-295-2012.
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Abstract. Earthquakes registering magnitudes Md = 4.5 and 4.7 struck the city of Konya, Central Anatolia, on 10–11 September 2009, causing very slight damages. The earthquake epicenters were located at the east of Sille District along the Konya Fault Zone, a dip-slip fault. The nature and seismicity of the fault zone indicates that it is capable of producing earthquakes of moderate magnitudes. This paper summarizes the geologic data along the fault zone and documents groundwater conditions and analyzes borehole and geotechnical data of the Konya city. The residential area of the city covers an area of approximately 1150 square kilometers and consists almost entirely of flat land except for a small part of rugged land in the southwestern corner. Groundwater and geotechnical data were collected and analyzed to evaluate the liquefaction potential of deposits under the Konya city. This preliminary investigation indicates that areas for liquefaction are generally limited to the eastern and east central parts of the city.
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Cawood, Peter A., Jeroen A. M. van Gool, and Greg R. Dunning. "Geological development of eastern Humber and western Dunnage zones: Corner Brook–Glover Island region, Newfoundland." Canadian Journal of Earth Sciences 33, no. 2 (February 1, 1996): 182–98. http://dx.doi.org/10.1139/e96-017.
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The Corner Brook–Glover Island region records the development of the internal domain of the Humber Zone and its relationship to the adjoining external domain and Dunnage Zone. The region preserves both the Laurentian margin basement–cover contact and the siliciclastic–carbonate transition within the cover sequence. Precambrian Grenville basement of the Corner Brook Lake Complex is the oldest lithostratigraphic unit and yielded a U/Pb zircon age of 1510 ± 6 Ma. Three main lithostratigraphic assemblages overlie basement: silicic and mafic igneous rocks of the Lady Slipper Pluton which yielded a U/Pb zircon age of [Formula: see text] Ma; siliciclastic lithologies which include the South Brook and Summerside formations; and carbonate-dominated sequences with clastic incursions which include the Port au Port, St. George, and Table Head groups, and the Breeches Pond, Irishtown, and Pinchgut formations. Dunnage Zone units include plutonic ultramafic to mafic rocks of the Grand Lake Complex, dated by U/Pb zircon from trondhjemite at 490 ± 4 Ma, volcanic and epiclastic rocks of the Glover Island Formation, and the Matthews Brook Serpentinite, the latter restricted to fault slivers within the Humber Zone sequence. The deformed Glover Island Granodiorite intrudes the Dunnage Zone rocks on Glover Island and is dated by U/Pb zircon and titanite at 440 ± 2 Ma. Little deformed Carboniferous sedimentary rocks unconformably overlie both Humber Zone and Dunnage Zone rock units. Timing of regional deformation and peak amphibolite-facies metamorphism in the eastern Humber Zone is constrained by isotopic data to the Early Silurian. In the Dunnage Zone, shear zones and foliation development both pre- and postdate the age of the Glover Island Granodiorite, with the later possibly temporally equivalent to deformation in the Humber Zone. Final juxtaposition of the two zones occurred during Carboniferous movement of the Cabot Fault.
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Alpak, Faruk O., and Tianhong Chen. "Dynamic effects of fault modeling on stair-step and corner-point grids." Journal of Petroleum Exploration and Production Technology 11, no. 3 (February 6, 2021): 1323–38. http://dx.doi.org/10.1007/s13202-020-01082-1.
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AbstractFault modeling has become an integral element of reservoir simulation for structurally complex reservoirs. Modeling of faults in general has major implications for the simulation grid. In turn, the grid quality control is very important in order to attain accurate simulation results. We investigate the dynamic effects of using stair-step grid (SSG) and corner-point grid (CPG) approaches for fault modeling from the perspective of dynamic reservoir performance forecasting. We have performed a number of grid convergence and grid-type sensitivity studies for a variety of simple, yet intuitive faulted flow simulation problems with gradually increasing complexity. We have also explored the added value of the multipoint flux approximation (MPFA) method over the conventional two-point flux approximation (TPFA) to increase the accuracy of reservoir simulation results obtained on CPGs. Effects of fault seal modeling on grid-resolution convergence and grid-type sensitivity have also been briefly examined. For simple geometries, both SSG and CPG can be used for fault modeling with similar accuracy in conjunction with the pillar-grid approach. This is evidenced by the fact that simulation results from SSG and CPG converge to identical solutions. SSG and CPG yield different results for more complex geometries. Simulation results approach to a converged solution for relatively fine SSGs. However, a SSG only provides an approximation to the fault geometry and reservoir volumes when the grid is coarse. On the other hand, non-orthogonality errors are increasingly evident in relatively more complex faulted models on CPGs and such errors cannot be addressed by grid refinement. It has been observed that MPFA partially addresses the discretization errors on non-orthogonal grids but only from the total flux accuracy perspective. However, transport related errors are still evident. Grid convergence behaviors and grid effects are quite similar with or without fault seal modeling (i.e., dedicated fault-zone modeling by use of scaled-up seal factors) for simple geometries. However, in more complex test cases, we have observed that it is more difficult to achieve converged results in conjunction with fault seal modeling due to increased heterogeneity of the underlying problem.
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Wen, Jian, Jiankuan Xu, and Xiaofei Chen. "The relations between the corner frequency, seismic moment and source dynamic parameters derived from the spontaneous rupture of a circular fault." Geophysical Journal International 228, no. 1 (August 27, 2021): 134–46. http://dx.doi.org/10.1093/gji/ggab346.
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SUMMARY The stress drop is an important dynamic source parameter for understanding the physics of source processes. The estimation of stress drops for moderate and small earthquakes is based on measurements of the corner frequency ${f_c}$, the seismic moment ${M_0}$ and a specific theoretical model of rupture behaviour. To date, several theoretical rupture models have been used. However, different models cause considerable differences in the estimated stress drop, even in an idealized scenario of circular earthquake rupture. Moreover, most of these models are either kinematic or quasi-dynamic models. Compared with previous models, we use the boundary integral equation method to simulate spontaneous dynamic rupture in a homogeneous elastic full space and then investigate the relations between the corner frequency, seismic moment and source dynamic parameters. Spontaneous ruptures include two states: runaway ruptures, in which the rupture does not stop without a barrier, and self-arresting ruptures, in which the rupture can stop itself after nucleation. The scaling relationships between ${f_c}$, ${M_0}$ and the dynamic parameters for runaway ruptures are different from those for self-arresting ruptures. There are obvious boundaries in those scaling relations that distinguish runaway ruptures from self-arresting ruptures. Because the stress drop varies during the rupture and the rupture shape is not circular, Eshelby's analytical solution may be inaccurate for spontaneous dynamic ruptures. For runaway ruptures, the relations between the corner frequency and dynamic parameters coincide with those in the previous kinematic or quasi-dynamic models. For self-arresting ruptures, the scaling relationships are opposite to those for runaway ruptures. Moreover, the relation between ${f_c}$ and ${M_0}$ for a spontaneous dynamic rupture depends on three factors: the dynamic rupture state, the background stress and the nucleation zone size. The scaling between ${f_c}$ and ${M_0}$ is ${f_c} \propto {M_0^{ - n}}$, where n is larger than 0. Earthquakes with the same dimensionless dynamic parameters but different nucleation zone sizes are self-similar and follow a ${f_c} \propto {M_0^{ - 1/3}}$ scaling law. However, if the nucleation zone size does not change, the relation between ${f_c}$ and ${M_0}$ shows a clear departure from self-similarity due to the rupture state or background stress.
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Xu, Changgui, Xiaofeng Du, Hongtao Zhu, Donghui Jia, Wei Xu, and Huan Lu. "Source-to-sink system and its sedimentary records in the continental rift basins: An example from the Paleogene in the Bohai Sea Area, China." Interpretation 5, no. 4 (November 30, 2017): ST35—ST51. http://dx.doi.org/10.1190/int-2017-0024.1.
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The “source-to-sink” concept originated in the study of global change and atmospheric pollution. In recent years, the concept of a source-to-sink system has been widely applied in continental margin sedimentary analysis. In our research, the idea of source-to-sink is applied to the continental rift basin sedimentary system in the Bohai Sea area. The idea emphasizes that the sedimentation dynamics, including erosion, transportation, and accumulation, are considered as a complete source-to-sink system. The sand-rich region often corresponds to a source-to-sink coupling system in a complex continental rift basin, which includes the effective provenance, high-efficiency routing system, and base-level transition. In addition, (1) the effective provenance can be subdivided into explicit and implicit provenance systems in which the implicit provenance system has been shown to be a significant advancement in reservoir prediction for the Bohai Sea area, (2) the sediment-transport pathways and slope-break zone constitute the routing systems, and (3) the base-level transition is one of the allogenic factors that controls the position of the sandstone distribution in a sequence. Based on a large number of previous studies and different characteristics of sequence-stratigraphic models in the Bohai Sea area, we have evaluated three types of source-to-sink systems, including the fault-steep slope, strike-slip fault slope, and gentle slope pattern. In addition, the fault-steep-slope source-to-sink coupling system can be further subdivided into four types, namely, the corner, relay ramps, fault-throw diminishment-type, and valley-type source-to-sink systems. The source-to-sink system of the gentle slope pattern includes the uplift axis valley-type source-to-sink system and the slope-valley-type source-to-sink system. A small-scale, thick layer of fan delta is formed in the fault-steep-slope zone. A continuous braided river delta is formed in the strike-slip fault slope zone. A large-scale, thin layer of braided river delta is formed in the gentle slope zone. The characteristics of source-to-sink systems in continental rift basins are established for the exploration or prediction of favorable zones in the study area, as well as in similar basins.
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McCann, William R. "On the earthquake hazards of Puerto Rico and the Virgin Islands." Bulletin of the Seismological Society of America 75, no. 1 (February 1, 1985): 251–62. http://dx.doi.org/10.1785/bssa0750010251.
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Abstract Puerto Rico and the Virgin Islands are located near the northeastern corner of the Caribbean seismic zone. Numerous large earthquakes have struck these islands, some with disastrous results. The 400-yr-long earthquake record of Puerto Rico describes shocks affecting nearly all portions of the island. The last destructive shock, in 1918 (7.5 MS), did not occur along the main seismic zone, but rather on an intraplate fault near Mona Canyon off the northwest coast. A possible great earthquake in 1787 (8 to 8.25 MS) appears to have occurred along the main seismic zone near the Puerto Rico Trench to the north of the island, but data for the event are scarce. A disastrous earthquake in the Virgin Islands (1867, 7.5 MS) also occurred on an intraplate fault. This fault is one of a series that bound the Anegada Trough separating Saint Croix from the main chain of the Virgin Islands. Seafloor morphology, microearthquakes, and the record of historic earthquakes define a zone of deformation extending from the Puerto Rico Trench, northeast of the Virgin Islands, trending southwest along the Anegada Trough and then westerly along the Muertos Trough. The Muertos Trough is the locus of convergence between the floor of the Caribbean Sea and Puerto Rico. Maximum dimensions of future large earthquakes are inferred from sizes of blocks in the Anegada and Muertos Troughs as well as Mona Canyon. Shocks as large as 7.5 can occur on these intraplate faults. Although strain rates on these faults may be an order of magnitude less than on faults in the Puerto Rico Trench, the large number of potential sources suggest that damaging earthquakes in this part of the Caribbean can come from either the Puerto Rico Trench or the intraplate faults with nearly equal probability.
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Rong, Yufang, Xiwei Xu, Jia Cheng, Guihua Chen, Harold Magistrale, and Zheng-Kang Shen. "A probabilistic seismic hazard model for Mainland China." Earthquake Spectra 36, no. 1_suppl (April 15, 2020): 181–209. http://dx.doi.org/10.1177/8755293020910754.
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We construct a probabilistic seismic hazard model for mainland China by integrating historical earthquakes, active faults, and geodetic strain rates. We delineate large seismic source zones based on geologic and seismotectonic characteristics. For each source zone, a tapered Gutenberg–Richter (TGR) distribution is used to model the total seismic activity rates. The TGR a- and b-values are calculated using a new earthquake catalog, while corner magnitudes are constrained using the seismic moment rate inferred from a geodetic strain rate model. For hazard calculations, the total TGR distribution is split into two parts, with smaller ( MW < 6.5) earthquakes being distributed within the zone using a smoothed seismicity method, and larger earthquakes put both onto active faults, based on fault slip rates and dimensions, and into the zone as background seismicity. We select ground motion models by performing residual analysis using ground motion recordings. Site amplifications are considered based on a site condition map developed using geology as a proxy. The resulting seismic hazard is consistent with the fifth-generation national seismic hazard model for most major cities.
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Li, Yao Bin. "The Integrated Control Countermeasures on Floor Heave of Broken Soft Rock with High Ground Stress." Advanced Materials Research 875-877 (February 2014): 2259–63. http://dx.doi.org/10.4028/www.scientific.net/amr.875-877.2259.
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The floor heave is one of the key issues of surrounding rock stability control during the deep well mining process. To solve the problem about floor heave occupying the most of roof and floor convergence deformation, the author analyzed the engineering geological conditions of broken surrounding rock and the floor heave features in PanEr Coal Mine East 2 mining area when it through the fault zone with high pressure. It pointed out that we should make full use of the reinforcement of the roof and laneway's side to limit the deformation of the floor, and make use of overbreak, prestressed anchor cable, bottom corner bolt, deep hole grouting and backfill as direct bottom control countermeasures.
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Rebollar, Cecilio J. "Source parameters of the Ensenada Bay earthquake swarm, Baja California, Mexico." Canadian Journal of Earth Sciences 22, no. 1 (January 1, 1985): 126–32. http://dx.doi.org/10.1139/e85-010.
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Seismic data collected from the Ensenada Bay earthquake swarm of late 1981 were used to calculate the spectra of ground displacement. Data from the stations of Ensenada (ENX) and Cerro Bola (CBX), at epicentral distances of 14 and 57 km, respectively, were used to evaluate source parameters. The focal depths determined for these events were less than 10 km. The focal mechanism was a strike-slip fault type, with the plane of motion striking N52°W, parallel to the Agua Blanca Fault. Seismic moments ranging from 3.44 × 1019 to 5.99 × 1020 dyn∙cm (3.44 × 1014 to 5.99 × 1015 N∙cm) were estimated for events with local magnitudes in the range 1.7–2.3. The source dimensions were found to be 186 ± 36 m and the stress drops between 3 and 66 bar (0.3 and 6.6 MPa), comparable to results obtained in previous studies of shallow events (depths <10 km). The Ensenada swarm could be attributed to a localized zone of high-strain energy at the intersection of two faults. Ratios of P to S corner frequencies were evident for only five events; they were 1.39 ± 0.38. Magnitude and seismic moment from other studies were compared with the Ensenada data in the range of magnitudes 0–3. All the data can be accommodated by log M0 = 1.5 ML + (16.9 ± 1.1). The Ensenada earthquake swarm and the Victoria earthquake swarm, which occurred in the Mexicali valley in 1978, have similar source radii and corner frequencies for the same range of seismic moments.
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Chen, X., and R. E. Abercrombie. "Improved approach for stress drop estimation and its application to an induced earthquake sequence in Oklahoma." Geophysical Journal International 223, no. 1 (June 26, 2020): 233–53. http://dx.doi.org/10.1093/gji/ggaa316.
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SUMMARY We calculate source parameters for fluid-injection induced earthquakes near Guthrie, Oklahoma, guided by synthetic tests to quantify uncertainties. The average stress drop during an earthquake is a parameter fundamental to ground motion prediction and earthquake source physics, but it has proved hard to measure accurately. This has limited our understanding of earthquake rupture, as well as the spatio-temporal variations of fault strength. We use synthetic tests based on a joint spectral-fitting method to define the resolution limit of the corner frequency as a function of the maximum frequency of usable signal, for both individual spectra and the average from multiple stations. Synthetic tests based on stacking analysis find that an improved stacking approach can recover the true input stress drop if the corner frequencies are within the resolution limit defined by joint spectral-fitting. We apply the improved approach to the Guthrie sequence, using different wave types and signal-to-noise criteria to understand the stability of the calculated stress drop values. The results suggest no systematic scaling relationship of stress drop for M ≤ 3.1 earthquakes, but larger events (M ≥ 3.5) tend to have higher average stress drops. Some robust spatio-temporal variations can be linked to the triggering processes and indicate possible stress heterogeneity within the fault zone. Tight clustering of low stress drop events at the beginning stage of the sequence suggests that pore pressure influences earthquake source processes. Events at shallow depth have lower stress drop compared to deeper events. The largest earthquake occurred within a cluster of high stress drop events, likely rupturing a strong asperity.
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Tang, Meng, Xiangtao Kang, Jiachi Ren, Lin Gao, Zhenqian Ma, and Dezhong Kong. "Mining Stress Distribution and Gas Drainage Application of Coal Seam Group under Fault Influence." Geofluids 2022 (August 23, 2022): 1–22. http://dx.doi.org/10.1155/2022/8432024.
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The existence of fault structures often seriously endangers the safe production of coal mines. In order to ensure the safe and efficient production of close coal seam group mines under the influence of faults, it is of wide engineering significance to study the gas occurrence and extraction technology between coal seam groups under the influence of faults. In this study, the mining and gas drainage of 13817 working face in Yueliangtian Mine were taken as the research background. Combined with theoretical research, laboratory analysis, and numerical simulation analysis, the pressure relief range of coal seam and the evolution characteristics of surrounding rock stress were studied, the coal and gas comining system under the influence of faults was determined, the gas drainage technology was optimized, and the effect was investigated and analyzed. The results show that the gas pressure reduction zone is formed in the range of 20 m and 6 m of the lower wall of F1 fault, and the pressure relief effect is good in the range of 40 m above the roof of the working face to 20 m below the bottom plate during the advancing process. The optimized gas drainage technology has a good effect on gas control in coal seam group mining under the influence of faults. The absolute gas emission of the working face is reduced to 28~36 m3/min, the gas concentration in the upper corner of the mining face is about 0.6%, and the gas concentration of the return airflow is reduced to less than 0.5%. The gas extraction rate of No. 8 coal seam is 52.9%, and the gas content in the fault zone is reduced by 60%, realizing the safe and efficient comining of coal and gas. The research results have certain reference and application value for mine gas control with similar mining conditions.
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Blanke, Aglaja, Grzegorz Kwiatek, Thomas H. W. Goebel, Marco Bohnhoff, and Georg Dresen. "Stress drop–magnitude dependence of acoustic emissions during laboratory stick-slip." Geophysical Journal International 224, no. 2 (November 5, 2020): 1371–80. http://dx.doi.org/10.1093/gji/ggaa524.
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SUMMARY Earthquake source parameters such as seismic stress drop and corner frequency are observed to vary widely, leading to persistent discussion on potential scaling of stress drop and event size. Physical mechanisms that govern stress drop variations are difficult to evaluate in nature and are more readily studied in controlled laboratory experiments. We perform two stick-slip experiments on fractured (rough) and cut (smooth) Westerly granite samples to explore fault roughness effects on acoustic emission (AE) source parameters. We separate large stick-slip events that generally saturate the seismic recording system from populations of smaller AE events which are sensitive to fault stresses prior to slip. AE event populations show many similarities to natural seismicity and may be interpreted as laboratory equivalent of natural microseismic events. We then compare the temporal evolution of mechanical data such as measured stress release during slip to temporal changes in stress drops derived from AEs using the spectral ratio technique. We report on two primary observations: (1) In contrast to most case studies for natural earthquakes, we observe a strong increase in seismic stress drop with AE size. (2) The scaling of stress drop with magnitude is governed by fault roughness, whereby the rough fault shows a more rapid increase of the stress drop–magnitude relation with progressing large stick-slip events than the smooth fault. The overall range of AE sizes on the rough surface is influenced by both the average grain size and the width of the fault core. The magnitudes of the smallest AE events on smooth faults may also be governed by grain size. However, AEs significantly grow beyond peak roughness and the width of the fault core. Our laboratory tests highlight that source parameters vary substantially in the presence of fault zone heterogeneity (i.e. roughness and narrow grain size distribution), which may affect seismic energy partitioning and static stress drops of small and large AE events.
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Force, Eric. "Stratigraphic evolution of provenance in a thick conglomerate-dominated Carboniferous succession in the southern Isle Madame area, Nova Scotia, and paleogeographic implications." Atlantic Geology 50 (August 1, 2014): 104. http://dx.doi.org/10.4138/atlgeol.2014.006.
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Thick conglomerate-dominated sedimentary successions of the Horton and lower Windsor groups in the southern Isle Madame area show provenance variations with stratigraphic position, based on pebble counts, petrographic observations, and facies trends throughout the conglomeratic units. These coarse clastic sediments were deposited in a transtensional basin that formed south of a splay of the Minas Fault Zone, now repeated by younger faults in the study area. A stratigraphic section 1300 m thick that includes the base of the Horton Group was derived mostly, if not entirely, from units in the Avalonian Mira terrane to the east. Similar provenance indications continue stratigraphically upward in this section and elsewhere on Isle Madame through the thick lower and central parts of the Horton Group. In the upper part of the Horton Group, an influx of high-grade metamorphic and deformed plutonic clasts is recorded in the conglomerates, and the percentage of this material continues to increase above a dark fine-grained interval and into the overlying Windsor Group. The metamorphic clasts strongly resemble local basement rocksexposed as belts between conglomeratic domains in Isle Madame, indicating that these deeper crustal rocks were unroofed within the former basin in the late Tournaisian, resulting in redirected drainage patterns. Paleocurrent and facies information suggest that the Mira terrane sources were located to the northwest at the time of deposition. Hence, paleogeographic reconstruction for the area involves not only unroofing of the deeper crustal rocks, but also dextral transcurrent movement to place the appropriate parts of the Mira terrane at the northwestern corner of exposed parts of the basin. This movement was along a subsequently deformed part of the Minas Fault Zone.
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Hooks, Benjamin Patrick. "The Role of Surface Processes in Partitioning of Strain and Uplift, St. Elias Orogen, Southern Alaska." Earth Science Research 5, no. 1 (January 27, 2016): 76. http://dx.doi.org/10.5539/esr.v5n1p76.
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<span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">Three-dimensional thermo-mechanical numerical simulations of the ongoing Yakutat–North America collision are used to identify the role of surface processes in triggering localized rapid uplift, exhumation, and strain observed within the St. Elias orogen of southern Alaska. Thermochronological data reveal localized rapid exhumation associated with the Seward-Malaspina and Hubbard Glaciers within a tectonic corner structure where transpressional motion to the south along the Fairweather Fault system transitions to shortening to the north and west within the active fold-and-thrust belt of the St. Elias orogen. The modeled deformation patterns are characteristic of oblique convergence within a tectonic corner, recording the transition from simple shear to contractional strain within a zone spatially consistent with the highest exhumation rates suggesting the corner geometry is the primary control of strain partitioning.</span><span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">The relative roles of surface-related processes versus tectonics-related processes in the development of this pattern of deformation were tested with the inclusion of an erosional surface model. The presence of surface processes enhanced the uplift and development of a localized rapid exhumation. When spatially and temporally erosion models are employed, the location of maxima is shifted in response. This indicates that efficient erosion, and resultant deposition and material advection can influence the localization of strain and uplift.</span>
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Dreger, Douglas S., and Donald V. Helmberger. "Complex faulting deduced from broadband modeling of the 28 February 1990 Upland earthquake (ML = 5.2)." Bulletin of the Seismological Society of America 81, no. 4 (August 1, 1991): 1129–44. http://dx.doi.org/10.1785/bssa0810041129.
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Abstract The 1990 Upland earthquake was one of the first sizable local events to be recorded broadband at Pasadena, where the Green's functions appropriate for the path are known from a previous study. The synthetics developed in modeling the 1988 Upland sequence were available for use in rapid assessment of the activity. First-motion studies from the Caltech-USGS array data gave two solutions for the 1990 main shock based on the choice of regional velocity models. Although these focal mechanisms differ by less than 5° in strike and 20° rake, it proved possible to further constrain the solution using these derived Green's functions and a three-component waveform inversion scheme. We obtain from long-period waves a fault-plane solution of θ = 216°, δ = 77°, λ = 5.0°, M0 = 2.5 × 1024 dyne-cm, depth = 6 km, and a source duration of 1.2 sec, for which the orientation and source depth are in good agreement with the first-motion results of Hauksson and Jones (1991). Comparisons of the broadband displacement records with the high-pass Wood-Anderson simulations suggests the 1990 earthquake was a complicated event with a strong asperity at depth. Double point-source models indicate that about 30 per cent of the moment was released from a 9-km deep asperity following the initial source by 0.0 to 0.5 sec. Our best-fitting distributed fault model indicates that the timing of our point-source results is feasible assuming a reasonable rupture velocity. The rupture initiated at a depth of about 6 km and propagated downward on a 3.5 by 3.5 km (length by width) fault. Both the inversion of long-period waves and the distributed fault modeling indicate that the main shock did not rupture the entire depth extent of the fault defined by the aftershock zone. A relatively small asperity (about 1.0 km2) with a greater than 1 kbar stress drop controls the short-period Wood-Anderson waveforms. This asperity appears to be located in a region where seismicity shows a bend in the fault plane.
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Tsuchiyama, Ayako, Taka’aki Taira, Junichi Nakajima, and Roland Bürgmann. "Emergence of Low-Frequency Aftershocks of the 2019 Ridgecrest Earthquake Sequence." Bulletin of the Seismological Society of America 112, no. 2 (January 4, 2022): 750–62. http://dx.doi.org/10.1785/0120210206.
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ABSTRACT Low-frequency earthquakes (LFEs) generally have relatively stronger spectral components in the lower frequency range compared with what is expected for regular earthquakes based on their magnitude. LFEs generally occur in volcanic systems or deep (>∼15 km) in plate boundary fault zones; however, LFEs have also been observed in nonvolcanic, upper crustal settings. Because there are few studies that explore the spatiotemporal behaviors of LFEs in the shallow crust, it remains unclear whether the shallow-crustal LFEs reflect local attenuation in their immediate vicinity or differences in their source mechanism. Therefore, it is important to identify shallow-crustal LFEs and to characterize their spatiotemporal activity, which may also improve our understanding of LFEs. In this study, we focus on detecting shallow-crustal LFEs and explore the possible generation mechanisms. We analyze 29,646 aftershocks in the 2019 Ridgecrest, California, earthquake sequence, by measuring the frequency index (FI) to identify candidate low-frequency aftershocks (LFAs), while accounting for the magnitude dependency of the FI. Using small earthquakes (ML 1–3) recorded in the borehole stations to minimize the attenuation effects in near-surface layers, we identify 68 clear LFAs in total. Based on their distribution and comparisons with other seismic parameters measured by Trugman (2020), the LFAs possess distinct features from regular events in the same depths range, including low corner frequencies and low stress drops. Events in the close vicinity of LFAs exhibit lower average FI values than regular aftershocks, particularly if the hypocentral distance between an LFA and its neighbors is less than 1 km. Our results suggest that LFAs are related to local heterogeneity or a highly fractured fault zone correlated with an abundance of cross faults induced by the aftershock sequence at shallow depths. Zones of high pore-fluid pressure in intensely fractured fault zones could cause the bandlimited nature of LFAs and LFEs in general.
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Rebollar, Cecilio J., Luis Quintanar, Jaime Yamamoto, and Antonio Uribe. "Source process of the Chiapas, Mexico, intermediate-depth earthquake (Mw = 7.2) of 21 October 1995." Bulletin of the Seismological Society of America 89, no. 2 (April 1, 1999): 348–58. http://dx.doi.org/10.1785/bssa0890020348.
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Abstract On 21 October 1995, we recorded with a local array an earthquake that occurred at a depth of 165 km in the subduction zone of Chiapas. The Harvard focal mechanism solution indicates a normal fault responding to the down-dip tension of the subducted oceanic crust. This is the first intermediate-depth earthquake well recorded with accelerographs and seismometers in Southeastern Mexico. Peak ground accelerations (PGA) range from 21 to 436 cm/sec2 at hypocentral distances of 174 to 256 km, respectively. The recorded PGAs are larger than those of the Copala, Guerrero, earthquake of 14 September 1995, which was a shallow (16 km) thrust fault with a similar magnitude (Mw = 7.4). The large PGA generated by the Chiapas earthquake are probably due to an enhancement of the signals produced by the up-ward intraslab propagation of energy and are similar to those observed from other intermediate-depth earthquakes in the subduction zone of Japan (Molas and Yamazaki, 1995). The duration of the strongest shaking increases from about 10 sec in the southeast at the town of San Vicente (close to the Tacaná volcano) to nearly 20 sec in the northwest, in the city of Tuxtla Gutierrez located near the epicenter. Teleseismic P-wave inversion using the Harvard focal mechanism solution indicates that the seismic moment was released in three events with a total duration of about 20 sec. The results of the inversion indicate that the rupture propagated from the northwest to the southeast along a 30-km distance. From spectral analysis, we calculate a total seismic moment release of 5.2 ± 0.5 × 1019 N-m equivalent to an Mw = 7.1 magnitude event. Using three sources with an average depth of 150 km, we were able to reach a reasonable match of the first 40 sec of the displacement records recorded at the broadband seismic stations of Huatulco (HUIG) and Pinotepa Nacional (PNIG). For the station located in Tuxtla Gutierrez (TUXD), we used two sources, since only the first 5 sec were modeled. The amplitude spectrum at teleseismic distances follows a typical Brune's (1970) θ−2 model. We obtained a corner frequency of 0.045 Hz from the spectra, which is equivalent to a source radius of 15 km and a stress drop of 65 bars assuming a circular fault.
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Adiyaman, Özlem, and Jean Chorowicz. "Late Cenozoic tectonics and volcanism in the northwestern corner of the Arabian plate: a consequence of the strike-slip Dead Sea fault zone and the lateral escape of Anatolia." Journal of Volcanology and Geothermal Research 117, no. 3-4 (October 2002): 327–45. http://dx.doi.org/10.1016/s0377-0273(02)00296-2.
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Fehler, Michael, and W. Scott Phillips. "Simultaneous inversion for Q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock." Bulletin of the Seismological Society of America 81, no. 2 (April 1, 1991): 553–75. http://dx.doi.org/10.1785/bssa0810020553.
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Abstract An inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low-frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite. Assuming a ω−2 source model, the inversion fits the P-wave spectra of microearthquake waveforms to determine individual values of corner frequency and low-frequency spectral amplitude for each event and one average frequency-independent Q for all source-receiver paths. We also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra. The waveforms analyzed were recorded by a borehole seismometer. The P-wave Q was found to be 1070. For Q values as low as 600 and as high as 3000, the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a Q of 1070. Average stress drop was 3.7 bars. Seismic moments obtained from spectra ranged from 1013 to 1018 dyne-cm. The low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes. Spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock. Stress drops were found to be larger near the edges of the seismic zone, in regions that had not been seismically active during previous injections. The seismic moments determined from spectra were used to obtain a coda length-to-moment relation. Then, moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal-to-noise ratio. The constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions. The slope is so high that the seismic energy release is dominated by the large number of small events. In the absence of information about the number of events smaller than we studied, we cannot estimate the total seismic energy released by the hydraulic injection.
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Csontos, László, István Dunkl, Gábor Vakarcs, and Abid H. Abbaso. "Transversal folding in Himalaya foothill ranges." Földtani Közlöny 149, no. 3 (September 29, 2019): 255. http://dx.doi.org/10.23928/foldt.kozl.2019.149.3.255.
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The Himalayan foreland in N Pakistan, dissected by Main Frontal Thrust (MFT) and Main Boundary Thrust (MBT) contains spectacular salients and syntaxes. The lateral (N-S) boundaries between these salients and syntaxes around Kalabagh city and east-southeast of Islamabad were believed to host deep-seated lateral ramps with strike slip movements. However, seismic data in these two sectors suggest that there are N-S trending folds and locally east- or west-vergent thrusts that affect the Paleozoic-Paleogene cover of the Indian shield, as well as the Miocene-Pliocene molasse sediments. The proposed lateral ramps cannot be followed on the seismic and on maps either; instead, both maps and seismic data suggest folding, often on a regional scale of harder Paleo-Mesozoic-Paleogene and softer Oligo-Miocene-Pilo-Pleistocene cover. The NE corner of Surghar range is proposed to be formed of relaying thrust sheets with emergent heads composed of Paleozoic-Paleogene and its slightly detached Miocene molasse. These relaying imbricates are taken in a southward flexure generated by a major right lateral shear of a wide zone, where transpressive Riedel shears, en echelon anticlines and southwards flexed earlier thrust faults are the main elements (but a single, through-going Kalabagh fault is missing). The generation of mapped N-S trending folds and east-vergent thrusts preceded the formation of the wide shear zone and southwards flexing.Hazara syntaxis is interpreted as a major antiform that re-folded MBT and Panjal thrust around Oligo-Miocene molasse, itself forming an antiform (BOSSART ET AL. 1988). In our model we propose that the west-vergent Balakot thrust and deeper blind thrusts are in the core of this antiform. In the southern continuation we propose that folds in Miocene molasse continue from eastern Potwar region to western Kashmir and there appears no major break. These structures are also re-folded in a major antiform with N-S axial trend. Map analysis also suggests that N-S trending folds bending earlier main thrusts are occurring in a wide area south of the Indus-Tsangpo suture.Several independent geological and geophysical observations including mapping, seismic analysis, earlier measurements of strain axes and of paleomagnetic declinations suggest that the salients and syntaxes may have been much more linear in the past (although a total linearity is not realistic). It is proposed that the present-day undulating pattern may have been generated by N-S trending folds due to general (and episodic) E-W shortening. If the main fault zones were more linear, the relay pattern along their segments suggests a left lateral shear component along MBT and a mixed, locally left, locally right lateral component along MFT. Earlier (ZEITLER 1985) and now provided low temperature thermochronological ages strongly suggest a rather general episode of E-W shortening between 4-5 Ma for the whole northern Indian margin. However, there should have been original transversal dome formation as early as Oligocene (DIPIETRO ET AL. 2008). It is also clear that longer N-S shortening and shorter E-W shortening episodes should alternate eventually in a very short time frame, since earthquake focal mechanisms (LISA AND KHWAJA 2004, BURG ET AL. 2005) suggest the coexistence of E-W compression and NW-SE compression in Potwar.There are several potential explanations for generating E-W shortening and related structures in a general N-S shortening regime. Possibilities range from fault terminations of thrust faults at high angles in a particular zone (TREOLAR ET AL. 1992) to en echelon folding along a major right lateral E-W fault zone. However, we speculate that E-W shortening could be much more general, suggesting a mechanism that affects the whole of Indian plate. Possibly the best explanation is given by analogue models (REPLUMAZ ET AL. 2012) proposing major, slightly convergent confining boundaries. If applied to the northwards advance of India, the northwards converging boundaries generate secondary E-W shortening and east-or west-vergent orogens parallel to these boundaries.
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Peirce, C., A. H. Robinson, M. J. Funnell, R. C. Searle, C. J. MacLeod, and T. J. Reston. "Magmatism versus serpentinization—crustal structure along the 13°N segment at the Mid-Atlantic Ridge." Geophysical Journal International 221, no. 2 (January 29, 2020): 981–1001. http://dx.doi.org/10.1093/gji/ggaa052.
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SUMMARY A region of oceanic core complexes (OCCs) exists at 13°N on the Mid-Atlantic Ridge that is regarded as a type site. This site includes two OCCs at 13°20′N and 13°30′N, thought to be in the active and dying stages of evolution, and two together called the Ashadze Complex (centred at 13°05′N) that are considered to be relict. Here we describe the results of S-wave seismic modelling along an ∼200-km-long 2-D transect traversing, south-to-north, through both the Mercurius and Marathon fracture zones, the southern outside corner of the 13°N segment, the OCCs, the ridge axis deviation in trend centred at 13°35′N, and the youngest oceanic crust of the eastern ridge flank to the north. Our inversion model, and the corresponding Vp/Vs ratio, show that the majority of the crust beneath the 13°30′N OCC comprises metamorphosed lithologies that have been exhumed to the shallowest subseabed level, while basaltic lithologies underlie the 13°20′N OCC. The transition between these contrasting crustal structures occurs over a distance of <5 km, and extends to at least ∼2 km depth below seafloor. The northern and southern OCCs of the Ashadze Complex have contrasting structures at shallow depth, with the northern OCC having a faster S-wave velocity in the upper crust. A Vp/Vs ratio of >1.9 (and equivalent Poisson's ratio of >0.3) indicates exhumed and/or metamorphosed lithologies beneath the bathymetric depression between them and within the crust beneath the southern OCC. Between the northern and southern flanks of the Marathon fracture zone and northern flank of Mercurius fracture zone, the lower crust has a relatively low Vp/Vs ratio suggesting that the deformation associated with Marathon fracture zone, which facilitates fluid ingress, extends laterally within the lower crust. Marathon fracture zone itself is underlain by a broad zone of low S-wave velocity (∼2.0 km s−1) up to ∼20 km wide from the seabed to at least the mid-crust, that is mirrored in a high Vp/Vs ratio and lower density, particularly deeper than ∼1 km below seabed within its bathymetric footprint. Volcanic domains are highlighted by a low Vp/Vs ratio of <1.6 (and equivalent Poisson's ratio of <0.15). Our combined seismic and density models favour the localized model of OCC evolution. They also show a considerable ridge-parallel variability in the amount and distribution of magmatic versus metamorphosed crust. Our results suggest that the current focus of magmatism lies to the north of the 13°20′N OCC, where the magmatic accretion-type seabed morphology observed is mirrored in the pattern of microseismicity, suggesting that its inward-facing median-valley-wall fault may link to the 13°20′N OCC detachment surface. Magmatism and active faulting behind (to the west) the footwall breakaway of the 13°30′N OCC, and the microseismicity concentrated in a band along its southern flank, suggest a readjustment of ridge geometry along axis is underway. As part of this, a transform offset is forming that will ultimately accommodate the 13°30′N OCC in its inside corner on the eastern flank of the ridge axis to the north.
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Jones, Stacie, Kurt Kyser, Matthew Leybourne, Robin Mackie, Adrian Fleming, and Daniel Layton-Matthews. "Paragenesis of gold mineralization at the Kiyuk Lake Project, Kivalliq Region, Nunavut, Canada." Canadian Mineralogist 59, no. 5 (September 1, 2021): 1133–65. http://dx.doi.org/10.3749/canmin.2000058.
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ABSTRACT Exploration for gold in Nunavut has been primarily focused on Archean greenstone belts in the north and coastal regions of the territory, resulting in large areas of underexplored terrain in the south. The Kiyuk Lake property is located in the underexplored southwest corner of the Kivalliq Region of Nunavut within the Hearne domain of the ∼1.9 Ga western Churchill Province. The property is hosted by Proterozoic calc-silicate and clastic sedimentary units of the Hurwitz Group (<2.4–1.9 Ga) and the unconformably overlying Kiyuk Group (1.9–1.83 Ga). Gold mineralization in Proterozoic sedimentary rocks is rare in the Canadian Shield, so the Rusty Zone at Kiyuk Lake presents a unique opportunity to study the enigmatic gold mineralization hosted in such sedimentary rocks. Mineralization at the Rusty Zone is hosted by an immature lithic wacke cut by thin intermediate dikes that are associated with hydrothermal breccias composed of Fe-carbonate, calcite, calcic-amphibole, Fe-sulfide, Fe-oxide minerals, and gold. Textural and timing relationships suggest that the gold mineralization is post-sedimentary and syn- to post-intrusion of intermediate dikes. Stable isotope thermometry suggests that mineralization took place between 450 and 600 °C, and geochronological studies indicate that the intrusion and mineralization occurred before or about 1.83 Ga. Using basement breaching thrusts faults as conduits to the surface, over-pressurization along a later normal fault is thought to be the primary cause for the localized breccia pipe that controls gold mineralization. The hydrothermal fluids are postulated to be volatile-rich aqueous solutions exsolved from a source of cooling magmas at depth. Although sub-economic at present, the occurrence of high-grade gold in a Paleoproterozoic basin such as Kiyuk Lake could signal a new opportunity for exploration for gold in the Canadian Shield.
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Yang, Wenzheng, and Yehuda Ben-Zion. "Corner frequency ratios ofPandSwaves and strain drops of earthquakes recorded by a tight network around the Karadere segment of the North Anatolian Fault Zone: evidence for non-classical source processes." Geophysical Journal International 205, no. 1 (February 16, 2016): 220–35. http://dx.doi.org/10.1093/gji/ggv560.
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Peirce, C., A. H. Robinson, A. M. Campbell, M. J. Funnell, I. Grevemeyer, N. W. Hayman, H. J. A. Van Avendonk, and G. Castiello. "Seismic investigation of an active ocean–continent transform margin: the interaction between the Swan Islands Fault Zone and the ultraslow-spreading Mid-Cayman Spreading Centre." Geophysical Journal International 219, no. 1 (June 20, 2019): 159–84. http://dx.doi.org/10.1093/gji/ggz283.
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SUMMARY The Swan Islands Transform Fault (SITF) marks the southern boundary of the Cayman Trough and the ocean–continent transition of the North American–Caribbean Plate boundary offshore Honduras. The CAYSEIS experiment acquired a 180-km-long seismic refraction and gravity profile across this transform margin, ∼70 km to the west of the Mid-Cayman Spreading Centre (MCSC). This profile shows the crustal structure across a transform fault system that juxtaposes Mesozoic-age continental crust to the south against the ∼10-Myr-old ultraslow spread oceanic crust to the north. Ocean-bottom seismographs were deployed along-profile, and inverse and forward traveltime modelling, supported by gravity analysis, reveals ∼23-km-thick continental crust that has been thinned over a distance of ∼70 km to ∼10 km-thick at the SITF, juxtaposed against ∼4-km-thick oceanic crust. This thinning is primarily accommodated within the lower crust. Since Moho reflections are not widely observed, the 7.0 km s−1 velocity contour is used to define the Moho along-profile. The apparent lack of reflections to the north of the SITF suggests that the Moho is more likely a transition zone between crust and mantle. Where the profile traverses bathymetric highs in the off-axis oceanic crust, higher P-wave velocity is observed at shallow crustal depths. S-wave arrival modelling also reveals elevated velocities at shallow depths, except for crust adjacent to the SITF that would have occupied the inside corner high of the ridge-transform intersection when on axis. We use a Vp/Vs ratio of 1.9 to mark where lithologies of the lower crust and uppermost mantle may be exhumed, and also to locate the upper-to-lower crustal transition, identify relict oceanic core complexes and regions of magmatically formed crust. An elevated Vp/Vs ratio suggests not only that serpentinized peridotite may be exposed at the seafloor in places, but also that seawater has been able to flow deep into the crust and upper mantle over 20–30-km-wide regions which may explain the lack of a distinct Moho. The SITF has higher velocities at shallower depths than observed in the oceanic crust to the north and, at the seabed, it is a relatively wide feature. However, the velocity–depth model subseabed suggests a fault zone no wider than ∼5–10 km, that is mirrored by a narrow seabed depression ∼7500 m deep. Gravity modelling shows that the SITF is also underlain, at >2 km subseabed, by a ∼20-km-wide region of density >3000 kg m−3 that may reflect a broad region of metamorphism. The residual mantle Bouguer anomaly across the survey region, when compared with the bathymetry, suggests that the transform may also have a component of left-lateral trans-tensional displacement that accounts for its apparently broad seabed appearance, and that the focus of magma supply may currently be displaced to the north of the MCSC segment centre. Our results suggest that Swan Islands margin development caused thinning of the adjacent continental crust, and that the adjacent oceanic crust formed in a cool ridge setting, either as a result of reduced mantle upwelling and/or due to fracture enhanced fluid flow.
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Klinger, Adam G., and Maximilian J. Werner. "Stress drops of hydraulic fracturing induced microseismicity in the Horn River basin: challenges at high frequencies recorded by borehole geophones." Geophysical Journal International 228, no. 3 (November 15, 2021): 2018–37. http://dx.doi.org/10.1093/gji/ggab458.
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SUMMARY The ground motions caused by seismicity associated with fluid injection can pose a significant hazard. Borehole geophone arrays can provide access to tiny seismic events, which can extend the investigated magnitude range. However, the high frequency phase arrivals (i.e., >100 Hz) also present challenges associated with high frequency cut-offs (fmax), stronger attenuation and resonances within geophones. These effects limit our ability to accurately constrain attenuation models and high frequency source parameters. We investigate 112 −0.6 $\le \, M_{\rm w}\, \le$ 0.7 seismic events and calculate corner frequencies and stress drops from 90 of these events recorded during hydraulic fracturing treatment in the Horn River basin, British Columbia. High frequency resonances (>250 Hz) caused by spurious frequency excitation and/or coupling issues can significantly distort the shape of phase arrival spectra and affect source parameter estimates. Critically, resonances vary in strength between (nearly) colocated events, which may compromise the validity of a spectral ratio approach. For stations showing the cleanest spectra, the Brune model provides a decent fit to the displacement spectra. However, bandwidth limitations, low signal-to-noise ratios, high frequency cut-offs and significant attenuation still hinder our ability to retrieve high frequency source parameters. We find that a frequency independent Qp = 180 ± 40 provides a reasonable model for crustal attenuation but the large uncertainty caused by resonances prevents a robust constraint. From those events that show the best fits, we find a mean Madariaga corner frequency of 210 Hz ± 30 from P-phase arrivals, which is in the range of expected values if self-similarity extends into negative magnitudes. We also calculate a mean stress drop of 1.6 MPa ± 1.2, which is within the tectonic range but slightly lower than other deeper regional studies, which can be explained by lower effective stresses and/or a lower crustal shear strength. We find no evidence for a change in stress drop with depth or distance from the point of injection. A plausible explanation is that effective stresses are lowered relatively quickly over the entire fault zone via direct hydraulic connections. However, the large uncertainties make it difficult to interpret source parameter variability in detail. For high resolution monitoring and source properties of microseismicity, there is an urgent need for high quality high frequency recordings unaffected by spurious frequencies.
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Burke, Kenneth B. S., Robert J. Wetmiller, Maurice Lamontagne, M. Jeffrey Carr, and Craig Hickey. "Microearthquake survey of the Miramichi, New Brunswick, epicentral region, 1985." Canadian Journal of Earth Sciences 26, no. 12 (December 1, 1989): 2567–77. http://dx.doi.org/10.1139/e89-219.
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A survey of the continuing microearthquake activity in the 1982 Miramichi earthquake epicentral region of central New Brunswick took place between July 3 and August 19, 1985. MEQ-800 analog seismographs were deployed at six recording stations for the 47 day period of the survey. Three BakPak digital seismographs were added to the network on July 23, two at the same locations as analog units and one at a seventh site.Three hundred and twenty-five microearthquakes were recorded during the survey. The activity was episodic, with days of few earthquakes being followed by periods when events clustered together in miniswarms. Coda-magnitude relationships for five stations were established from regression analysis of scaled coda lengths of events on the MEQ 800 records and Nuttli magnitudes determined at an Eastern Canadian Telemetered Network station KLN. Only 21 of the events had coda magnitudes (Mc) greater than 0, the largest being 2.0. The larger magnitude earthquakes occurred in zones where there had been little preceding activity. The highest rate of activity was associated with the northeastern corner of the 1982 aftershock zone. Sporadic activity was also recorded from the western side of the zone.Composite P-nodal solutions for three subzones are consistent with the conjugate pattern of thrust faulting obtained in previous studies, except for rotation of fault-plane strikes from northerly to northwesterly directions for two of the subzones. It is remarkable that the pattern of activity first mapped by the 1982 aftershock surveys has remained relatively stationary over the subsequent 3½ year period.Un levé microséismique de l'activité courante dans la région épicentrale du tremblement de terre de Miramichi au Nouveau-Brunswick de janvier 1982 a été effectué entre le 3 juillet et le 19 août 1985. Des séismographes portatifs (MEQ 800) furent installés à six stations pendant une période de 47 jours. Trois séismographes numériques (BakPak) furent ajoutés au réseau le 23 juillet : deux sur sites de MEQ 800's et l'autre sur un septième emplacement.
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Calderoni, Giovanna, Anna Gervasi, Mario La Rocca, and Guido Ventura. "Strike-Slip Earthquakes at the Northern Edge of the Calabrian Arc Subduction Zone." Seismological Research Letters, December 2, 2020. http://dx.doi.org/10.1785/0220200251.
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Abstract We analyzed earthquakes of a swarm started in October 2019 in the Tyrrhenian Sea, at the northern border of the Calabrian arc subduction zone. The swarm is located in the same area where a subduction-transform edge propagator (STEP) shear- zone -oriented east–west is recognized from ocean floor morphology and submarine volcanoes. We computed focal mechanism, relative location, stress drop, corner frequency, and source directivity of the mainshock Mw 4.4 and of some aftershocks in the local magnitude range 2.3–3.7. Results indicate clearly that the mainshock occurred on a northwest–southeast-oriented fault, with right-lateral strike-slip motion, and it was characterized by a strong directivity of the rupture propagation from northwest to southeast. On the contrary, most of aftershocks were located on another strike-slip fault oriented northeast–southwest and had left-lateral kinematics. The kinematic features of these earthquakes indicate a strain field with the P-axis oriented north–south and the T-axis oriented east–west. Fault directions and stress field are in good agreement with the theoretical fracture model of shear zones associated with a STEP.
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Wang, Hongwei, and Ruizhi Wen. "Earthquake Source Characteristics and S-Wave Propagation Attenuation in the Junction of the Northwest Tarim Basin and Kepingtage Fold-and-Thrust Zone." Frontiers in Earth Science 8 (December 22, 2020). http://dx.doi.org/10.3389/feart.2020.567939.
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We separated the propagation path attenuation and source spectra from the S-wave Fourier amplitude spectra of the observed ground motions recorded during 46 small-to-moderate earthquakes in the junction of the northwest Tarim Basin and Kepingtage fold-and-thrust zone, mainly composed of two Jiashi seismic sequences in 2020 and 2018. Slow seismic wave decay was observed as the distance increased, while the quality factor regressed as 60.066 f0.988 for frequency f = 0.254–30 Hz reflects the strong anelastic attenuation in the study region. We estimated the stress drops for the 46 earthquakes under investigation from the preferred corner frequencies and seismic moments by fitting the inverted source spectra and the theoretical ω-square model. The relationship between seismic moment and corner frequency and the dependence of the stress drop on the moment magnitude reveal the breakdown of earthquake self-similar scaling for the events in this study. The temporal variation in stress drops indicates that the mainshock plays a short-term role in the source characteristics of the surrounding earthquakes. Aftershocks immediately following the mainshock show a low stress release and then gradually recover in a short time. The healing process for the fractured fault in the mainshock may be one reason for the stress drop recovery of the aftershock. The foreshock with the low stress release occurring in the high-heterogeneity fault zone may motivate the following occurrence of the largest magnitude mainshock with a high stress drop. We inferred that the foreshock-mainshock behavior, including several moderate events, may be predisposed to occur in our study region characterized by an inhomogeneous crust.
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Koptev, Alexander, Matthias Nettesheim, Sarah Falkowski, and Todd A. Ehlers. "3D geodynamic-geomorphologic modelling of deformation and exhumation at curved plate boundaries: Implications for the southern Alaskan plate corner." Scientific Reports 12, no. 1 (August 22, 2022). http://dx.doi.org/10.1038/s41598-022-17644-8.
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AbstractPlate corners with extreme exhumation rates are important because they offer a perspective for understanding the interactions between tectonics and surface processes. The southern Alaskan margin with its curved convergent plate boundary and associated zones of localized uplift is a prime location to study active orogeny. Here, we present the results of fully-coupled thermo-mechanical (geodynamic) and geomorphologic numerical modelling, the design of which captures the key features of the studied area: subduction of oceanic lithosphere (Pacific plate) is adjacent to a pronounced asymmetric indenter dipping at a shallow angle (Yakutat microplate), which in turn is bounded to the east by a dextral strike-slip shear zone (Fairweather fault). The resulting first-order deformation/rock uplift patterns show strong similarities with observations. In particular, relatively young thermochronological ages are reproduced along the plate-bounding (Fairweather) transform fault and in the area of its transition to convergence (the St. Elias syntaxis). The focused exhumation of the Chugach Core also finds its equivalent in model predicted zones of high rock uplift rates in an isolated region above the indenter. From these results, we suggest that the general exhumation patterns observed in southern Alaska are controlled by mutually reinforcing effects of tectonic deformation and surface erosion processes.
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Bansal, Brijesh K., Anup K. Sutar, and Mithila Verma. "The 2020 earthquake sequence and seismic hazard scenario of Mizoram state in northeast India." Frontiers in Earth Science 10 (September 28, 2022). http://dx.doi.org/10.3389/feart.2022.985394.
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The Mizoram state of India lies in close proximity to the active Indo-Burma subduction zone and had experienced several moderate to large earthquakes, including the M7 event in 1938. Since 2015, only two events with 5<M<6 have occurred in the area, however, a sudden enhancement of earthquake activity (M3.0–M5.7) was observed from June to August 2020 in the eastern part of the Mizoram state, including the four events of M ≥ 5.0. We analysed the waveform data of 21 events recorded by the local and regional BBS to estimate the source parameters. The focal depth of these events varies from 13 to 45 km, while other parameters such as corner frequency, source radius, stress drop, and scalar seismic moment of the events are found in the range of 0.45–3.36 Hz, 0.77–5.58 km, 1.3–193 bars, and 3.98107E+13 to 6.30957E+17 Nm, respectively. The seismicity pattern shows two distinct clusters along the well-demarcated faults in the region, and most of them are generated by strike-slip movements. The Churachandpur-Mao Fault (CMF) is found to be the most active tectonic element in the study area. Hence, an M8 event has been simulated on the same fault using the stochastic simulation technique. The technique was validated by simulating the three M+5 events on the same source zone and comparing the simulated PGA, frequency, and response spectrum with the observed data. The simulation reveals that a PGA ∼480 gals is expected near the fault zone. The easternmost districts of Mizoram, such as Champai, Serchhip, Lunglei, Saiha, and Aizawl, may experience severe PGA (250–450 gals). The response spectral acceleration corresponding to single-storey, double-storey, 3–4 storey, and 5–6 storey buildings has also been estimated in the present study and it is found to vary in the range of 1,400–200 gals. The result of the present study will be useful in various engineering applications and help reduce the loss of lives and damage to infrastructure due to future large events in the region.
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Henriksen, Niels, and A. K. Higgins. "Descriptive text to Geological map of Greenland, 1:500 000, Dove Bugt, Sheet 10." Geological Survey of Denmark and Greenland (GEUS) Bulletin, October 1, 2009, 1–32. http://dx.doi.org/10.34194/geusb.v4.4581.
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The Dove Bugt 1:500 000 scale geological map sheet covers a segment of the East Greenland
Caledonian orogen extending between latitudes 75°–78°N and longitudes 16°–29°W. The region was mapped in the summers of 1988–1990 as part of a regional Survey mapping programme, and the map sheet was printed in 1997.
The region covered by the Dove Bugt map sheet is dominated by Palaeoproterozoic gneiss complexes, with smaller amounts of Mesoproterozoic and Neoproterozoic metasedimentary rocks, and isolated strips of Palaeoproterozoic and Lower Palaeozoic sedimentary rocks. All these rock units have been reworked to a varying degree during the Caledonian orogeny. Post-Caledonian sedimentary rocks occur in the south-east corner of the map sheet area and as narrow, fault-bounded enclaves elsewhere, while Palaeogene basaltic lavas and sills crop out on the island of Shannon.
The rocks of the Caledonian orogen form a number of major thrust domains. The most extensive and structurally lowest is the Nørreland thrust sheet which is characterised by lenses and layers of medium-temperature, high-pressure eclogites. The Western thrust belt occupies a broad zone of eastern Dronning Louise Land that comprises Palaeoproterozoic gneiss complexes interleaved with Palaeoproterozoic and Palaeozoic metasedimentary rocks. This thrust domain is separated from the foreland rocks of western Dronning Louise Land by the Imbricate thrust zone. In the south-west part of the map sheet the highest structural domain, the Hagar Bjerg thrust sheet comprises three rock sequences: crystalline gneisses, the Mesoproterozoic Smallefjord sequence and the Neoproterozoic Eleonore Bay Supergroup.
The crystalline gneiss complexes that dominate the map sheet area and make up a significant proportion of the different Caledonian thrust domains have all yielded protolith ages of c . 2 Ga. They are attributed to a major period of crust formation in the Palaeoproterozoic. The gneisses have been variably affected by Caledonian deformation and metamorphism.
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Henriksen, Niels, and A. K. Higgins. "Descriptive text to Geological map of Greenland, 1:500 000, Dove Bugt, Sheet 10." GEUS Bulletin, October 1, 2009, 1–32. http://dx.doi.org/10.34194/geusm.v4.4581.
Full textAbstract:
NOTE: This Map Description was published in a former series of GEUS Bulletin. Please use the original series name when citing this series, for example:
Henriksen, N., & Higgins, A. (2009). Descriptive text to Geological map of Greenland, 1:500 000, Dove Bugt, Sheet 10. Geological Survey of Denmark and Greenland Map Series 4, 1-32. https://doi.org/10.34194/geusm.v4.4581
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The Dove Bugt 1:500 000 scale geological map sheet covers a segment of the East Greenland Caledonian orogen extending between latitudes 75°–78°N and longitudes 16°–29°W. The region was mapped in the summers of 1988–1990 as part of a regional Survey mapping programme, and the map sheet was printed in 1997.
The region covered by the Dove Bugt map sheet is dominated by Palaeoproterozoic gneiss complexes, with smaller amounts of Mesoproterozoic and Neoproterozoic metasedimentary rocks, and isolated strips of Palaeoproterozoic and Lower Palaeozoic sedimentary rocks. All these rock units have been reworked to a varying degree during the Caledonian orogeny. Post-Caledonian sedimentary rocks occur in the south-east corner of the map sheet area and as narrow, fault-bounded enclaves elsewhere, while Palaeogene basaltic lavas and sills crop out on the island of Shannon.
The rocks of the Caledonian orogen form a number of major thrust domains. The most extensive and structurally lowest is the Nørreland thrust sheet which is characterised by lenses and layers of medium-temperature, high-pressure eclogites. The Western thrust belt occupies a broad zone of eastern Dronning Louise Land that comprises Palaeoproterozoic gneiss complexes interleaved with Palaeoproterozoic and Palaeozoic metasedimentary rocks. This thrust domain is separated from the foreland rocks of western Dronning Louise Land by the Imbricate thrust zone. In the south-west part of the map sheet the highest structural domain, the Hagar Bjerg thrust sheet comprises three rock sequences: crystalline gneisses, the Mesoproterozoic Smallefjord sequence and the Neoproterozoic Eleonore Bay Supergroup.
The crystalline gneiss complexes that dominate the map sheet area and make up a significant proportion of the different Caledonian thrust domains have all yielded protolith ages of c. 2 Ga. They are attributed to a major period of crust formation in the Palaeoproterozoic. The gneisses have been variably affected by Caledonian deformation and metamorphism.